Aluminum furnace charging methods

ABSTRACT

There is provided a method of charging an electrolyte bath containing aluminum oxide for the manufacture of aluminum by smelt electrolysis, with fresh supplies of aluminum oxide as the electrolyte is depleted thereof. A pre-determined store of aluminum oxide is constantly maintained on the crust covering the bath. This crust is then partially broken by raising and lowering the anode at predetermined intervals during the electrolysis to permit the oxide resting on the crust to enter the bath, thereby to increase the aluminium oxide content of said bath.

United States Patent Waenerlu nd ALUMINUM FURNACE CHARGING METHODS Appl. No: 469,701

llli 3,919,058

[ Nov. 11, 1975 FOREIGN PATENTS OR APPLICATIONS LHSUWJU WW6? United Kingdom.. v v i l 204/67 LSSHJST ll/l97l Germain i i i i i i i 204/67 (wUXbSo Wl HX United Kingdomw. 204/247 Primary liimliilwr-John Hi Mack Assisluu/ liimninw-Auron Weisstueh Anni-item Ago/11. or Firm-Vvaters. Schwartz it Nissen [57} ABSTRACT There is provided a method of charging an electrolyte [30] Forei n A lieation Prioritv Data g 2 pp g hath containing aluminum oxide for the manufacture Md} 73067 S of aluminum l1 smelt electrolysis. with fresh supplies of aluminum oxide as the electrolvte is depleted i i 1 I t C gZ /i, Z. 7;% 7?1 thereot A predetermined store of aluminum oxide Is 1 3' R eonstuntl maintained on the crust covering the huth. 0 are This crust is then partially broken h) raising and low ering the anode ut predetermined intervals during the Q t v References Clled ClCCU0l \'SIS to permit the oxide resting on the crust to UNITED STATES PATENTS enter the hz.ith thereby to increase the aluminium 3.632.488 1/1972 Decker et ul, iiiiiiiiiiiiiii iiiiii gin/(17 oxide content of said hath 3.664935 5/1972 Johnson .w 204/245 X a 3.631.229 8/1972 Lowe 204/245 x 4 2 Drawmg F'gures 5 ll! -I1 Ki ti U.S. Patent Nov. 11, 1975 ALUMINUM FURNACE CHARGING METHODS The present invention relates to a method of charging electrolysis smelting furnaces intended for the manufacture of aluminium and being of the type which comprise a vessel which forms the furnace cathode and which contains a molten bath comprising aluminium, formed by the electrolysis of aluminium oxide, and a molten electrolyte, such as cryolite, which has aluminium oxide dissolved therein, and a crust of solidified electrolyte and aluminium oxide located on top of said bath, and which furnaces further comprise at least one anode construction which is movable at least vertically and which has an electrode immersed in said electrolyte. The invention is primarily intended for application with furnaces operating with anodes of the Soderberg type and having vertical electrical contact bolts, although it can also be applied in conjunction with electrolysis furnaces which use other types of anodes, such as pre-baked anode blocks.

An object of the invention is to provide a novel and useful method of automatically charging aluminium oxide to the furnace, without the use of expensive or complicated auxiliary equipment.

To this end, it is proposed in accordance with the invention when charging furnaces of the aforementioned type in the manufacture of aluminium to partially break said crust by raising and lowering the anode construction whilst maintaining contact between said electrode and the molten electrolyte, thereby to cause aluminium oxide to enter the bath, and to charge along at least one side of the anode construction a quantity of aluminium oxide which corresponds to that quantity of aluminium oxide received locally by the bath at any point along said side so as to constantly maintain thereat a predetermined store of aluminium oxide to be electrolysed which covers the crust along said side of the anode construction.

So that the invention will be more readily understood and other features thereof made apparent, a method of charging electrolysis smelting furnaces for the manufacture of aluminium will now be described with reference to the accompanying drawing, in which FIG. 1 is a schematic vertical sectional view through an electrolysis smelting furnace suitable for carrying out the method of the invention and FIG. 2 is a side view of a part of the furnace shown in FIG. 1.

Like and coinciding elements shown in the two Figures are identified by the same reference numeral. There is shown in the drawing a trough-shaped vessel which contains a molten bath comprising a lower layer 11 consisting of aluminium, obtained by the electrolysis of aluminium oxide, and an upper layer 12 consisting of an aluminium oxide containing electrolyte. The electrolyte may comprise substantially molten cryolite. Incorporated in the bottom of the vessel are electrical contact devices (not shown) which are connected to the negative pole of a current source (not shown), so that the bottom of the tank forms a cathode for the electrolysis.

Immersed in the molten aluminium oxide containing electrolyte is an electrode body 14 enclosed in a casing 13. The electrode body, which is consumed during the electrolysis, is of the Soderberg type and is replenished in a conventional manner during the course of the electrolysis, by supplying fresh electrode mass thereto from above. The electrode body 14 is supported by a plurality of contact bolts 15 which are arranged in said body and which are suspended from an anode beam 16 connected to the positive pole of a current source (not shown). The casing 13 is also suspended from the anode beam, by means of jacks or adjustable holder de vices l7. Extending around the casing 13 is a gas collecting hood 18 for collecting the gases formed during the process of electrolysis. The hood 18 is connected by means of a line (not shown) to a suitable device for recovering or combusting the gases collected in said hood.

The anode l3, 14, the contact bolts 15, the anode beam 16, the holders l7 and the hood 18 together form a coherent anode construction which is vertically adjustably supported at the ends of the beam 16 by means of the schematically illustrated jacks 19 which in turn are supported by a frame 20, which is only partially illustrated.

As will be seen from FIG. 1, the anode construction 13-18 carries two magazines 2] which are capable of storing sufficient aluminium oxide to satisfy the requirements of the electrolysis furnace for a considerable period of time, for example 24 hours. With the illustrated embodiment the magazines 21 are carried by the casing 13, although said magazines could also be carried by some other suitable part of the anode construction or by the frame 20 or by some other appropriate stationary supporting device. Extending downwardly from the magazines 2], which are suitably spaced from the casing 13 as shown in FIG. 1, is a number of pipes 22 through which powderous aluminium oxide stored in the magazines can run freely down onto the crust 23 formed above the molten bath and comprising aluminium oxide and solidified electrolyte.

In accordance with the invention, the pipes 22 are arranged to discharge at such a distance above the crust and the horizontal extension of the discharge orifices of the pipes 22 along the adjacent side of the anode construction is of such magnitude and/or the pipes 22 are arranged in such close relationship relative to each other that overlapping fall cones are formed at the exit orifices of said pipes so that the crust 23 along said anode construction side is constantly kept covered with a supply 24 of aluminium oxide. These overlapping fall cones are seen in FIG. 2.

When practicing the method of the present invention while using the electrolysis furnace shown in the drawing, the anode construction 13-18 is raised and low ered by means of the jacks 19 whilst maintaining the contact between the electrolyte l2 and the enclosed electrode body 14. In this way the crust 23 is broken adjacent the hood 18, so that part of the crust together with part of the aluminium oxide resting on the crust passes down into the electrolyte l2 and is dissolved therein, thereby to raise the aluminium oxide content of the electrolyte. By permitting the aluminium oxide to flow freely from the magazines 21 via the pipes 22 so as constantly to maintain on the crust 23 a supply of aluminium oxide determined by the spaced apart relationship of the pipe orifices and the distance of said orifices from the crust and the angle of repose of the aluminium oxide supplied from said magazine there is always fed to any point located along the anode construction side or sides provided with magazine 21 a quantity of aluminium oxide which corresponds to that quantity of oxide received locally by the molten bath as the crust 23 is broken.

it has been found that when raising and lowering the anode construction the crust 23 tends to break at those places where the crust is thin; at which places there consequently exists a certain degree of local overheating in the electrolysis bath. Such local overheating, however, is rapidly eliminated with the method of the present invention, since when charging the furnace with aluminium oxide in accordance with the invention a relatively large quantity of aluminium oxide is fed down into the electrolyte at the overheated zones and therewith lowers the temperature at said zones.

in accordance with the invention, charging of the furnace is effected suitably at such close time intervals and the quantities of aluminium oxide charged are of such insignificant magnitude that the content of dissolved aluminium oxide of the electrolyte 12 is maintained at a relatively constant level favourable to the electrolysis process, whereby the maximum current yield can be obtained. it has been found expedient to charge the furnace once or twice each hour, wherein the anode construction is suitably raised and lowered only once or a few times in a manner such that the crust 23 is only broken in the region adjacent the anode construction. If the anode construction is provided with an additional array of jacks in order to hold the anode casing still when making regulations to the funace, these additional jacks must be disengaged or the like when charging the furnace in accordance with the invention. The total extent of vertical movement executed by the anode construction during a furnace charging sequence is dependent on the depth to which the anode is immersed in the molten electrolyte and normally reaches to between and mm. In order to check, inter alia, the state of the electrolyte for example, it is expedient to sometimes permit for example once or twice per 24 hours the aluminium oxide content of the electrolyte 12 to fall to such an extent that a so-called anode effect occurs, that is to say a significant increase in voltage between the cathode 10 and the electrode 14. For this purpose, the magazines 21 or pipes 22 should be provided with means which enable communication between the magazines 21 and the stores 24 to be temporarily broken when so desired.

The charging movement of the anode construction l3-l8 can be obtained either by manually controlling the drive means of the jacks 19 or automatically by means of a programmed mechanism or data machine, for example arranged to initiate said charging movement at specific intervals in time.

The method of the present invention requires but the minimum of manual superintendance. since it is only necessary to fill the magazines 21 a few times each day and since the correct amount of aluminium oxide is constantly and automatically maintained on the crust 23. This affords a considerable saving in manpower, and owing to the free flow of aluminum oxide from the magazines 2] environmental problems in the form of leaking gas are avoided. The magazines constitute at 4 the same time a protection against heat radiation from the anode l3, 14, thereby making any work which must be carried out in the vicinity of the furnace more comfortable.

The invention is not restricted to the embodiments described and illustrated with reference to the accompanying drawing, but can be modified within the scope of the following claims.

I claim:

1. A method of charging electrolysis smelting furnaces for the manufacture of aluminum and being of the type which comprise a vessel which forms the furnace cathode and which contains a molten bath comprising aluminum, formed by the electrolysis of aluminum oxide and a molten electrolyte, which has aluminum oxide dissolved therein, and a crust of solidified electrolyte and aluminum oxide located on top of said bath, and which furnaces further comprise at least one anode construction which is movable vertically and having an electrode immersed in said electrolyte, and an aluminum oxide magazine having at least one supply line depending therefrom and discharging a substantially predetermined distance above the crust for supplying aluminum oxide to the crust along the length of at least one side of the anode construction, aluminum oxide being fed to the molten bath by partially breaking the crust by raising and lowering the anode construction whilst maintaining contact between said electrode and the molten electrolyte, the improvement comprising maintaining a constant free communication between said magazine and said crust during normal operation of the furnace thereby to provide an automatic flow of aluminum oxide to the crust in a quantity which corresponds to that quantity of aluminum oxide locally received by the molten bath at any point along at least said one side, and maintaining along at least said one side a predetermined store of aluminum oxide to be electrolyzed which covers the crust.

2. A method according to claim 1, characterized in that there is used a plurality of supply pipes depending from the magazine, the distance between adjacent pipe orifices and between the pipe orfices and the crust being adapted so that the bases of the aluminium oxide cones formed on the exit side of said pipes partially overlap each other to continuously cover the crust along said side of said anode construction.

3. A method according to claim 1, wherein the anode construction comprises a gas collecting hood extending along said anode construction side, characterized in that aluminium oxide is charged to the furnace externally of the gas collecting hood.

4. A method according to claim 1 applied in conjunction with anode constructions having an anode casing which is movable relative the anode body, character' ized in that movement of the anode casing relative said anode body is prevented during the charging operation. a: a: 

1. A METHOD OF CHARGING ELECTROLYSIS SMELTING FURNANCES FOR THE MANUFACTURE OF ALUMINUM AND BEING OF THE TYPE WHICH COMPRISE A VESSEL WHICH FORMS THE FURNANCE CATHODE AND WHICH CONTAINS A MOLTEN BATH COMPRISING ALUMINUM, FORMED BY THE ELECTROLYSIS OF ALUMINUM OXIDE AND A MOLTEN ELECTROLYTE, WHICH HAS ALUMINUM OXIDE DISSOLVED THEREIN, AND A CRUST OF SOLIFIED ELECTROLYTE AND ALUMINUM OXIDE LOCATED ON TOP OF SAID BATH, AND WHICH FURNACES FURTHER COMPRISES AT LEAST ONE ANODE CONSTRUCTION WHICH IS MOVABLE VERTICALLY AND HAVING AN ELECTRODE IMMERSED IN SAID ELECTROLYTE, AND AN ALUMINUM OXIDE MAGAZINE HAVING AT LEAST ONE SUPPLY LINE DEPENDING THEREFROM AND DISCHARGING A SUBSTANTIALLY PREDETERMINED DISTANCE ABOVE THE CRUST FOR SUPPLYING ALUMINUM OXIDE TO THE CRUST ALONG THE LENGTH OF AT LEAST ONE SIDE OF THE ANODE CONSTRUCTION, ALUMINUM OXIDE BEING FED TO THE MOLEN BATH BY PARTIALLY BREAKING THE CRUST BY RAISING AND LOWERING THE ANODE CONSTRUCTION WHILST MAINTAINING CONTACT BETWEEN SAID ELECTRODE AND THE MOLTEN ELECTROLYTE, THE IMPROVEMENT COMPRISING MAINTAINING A CONSTANT FREE COMMUNICATION BETWEEN SAID MAGAZINE AND SAID CRUST DURING NORMAL OPERATION OF THE FURNANCE THEREBY TO PROVIDE AN AUTOMATIC FLOW OF ALUMINUM OXIDE TO THE CRUST IN A QUANTITY WHICH CORRESPONDS TO THAT QUANTITY OF ALUMINUM OXIDE LOCALLY RECEIVED BY THE MOLTEN BATH AT ANY POINT ALONG AT LEAST SAID ONE SIDE, AND MAINTAINING ALONG AT LEAST SAID ONE SIDE A PREDETERMINED STORE A ALUMINUM OXIDE TO BE ELECTROLYZED WHICH COVERS THE CRUST.
 2. A method according to claim 1, characterized in that there is used a plurality of supply pipes depending from the magazine, the distance between adjacent pipe orifices and between the pipe orfices and the crust being adapted so that the bases of the aluminium oxide cones formed on the exit side of said pipes partially overlap each other to continuously cover the crust along said side of said anode construction.
 3. A method according to claim 1, wherein the anode construction comprises a gas collecting hood extending along said anode construction side, characterized in that aluminium oxide is charged to the furnace externally of the gas collecting hood.
 4. A method according to claim 1 applied in conjunction with anode constructions having an anode casing which is movable relative the anode body, characterized in that movement of the anode casing relative said anode body is prevented during the charging operation. 